Proceedings Article | 11 August 2000
KEYWORDS: Titanium, Modulators, Semiconducting wafers, Thin films, Diamond, Platinum, Gold, Interfaces, Lithium niobate, Waveguides
This paper describes the mechanical behavior of the evaporated layers between the thick gold electrode and the substrate in LiNbO3/Pt/Ti/Au/Au lithium niobate integrated optical waveguide modulator, using depth sensing diamond nanoindentation technique. In spite of its limitation in testing ultra thin films, this technique showed its usefulness in characterizing the recent application as well as integrated optical (IO), and MEMS devices. The mechanical properties of the evaporated layers such as hardness, elastic modulus, yield strength, and plastic deformation have been investigated by nanoindentation using a Berkovich indenter at a penetration depth of dequals100nm, and average values are given. It was found that the effect of the substrate on the film properties is negligible at penetration depth less tahn 20% of the film thickness, thus, the values of hardness and modulus are Eapproximately equals 20GPa, Happroximately equals 1GPa for the 20nm thin titanium film, Eapproximately equals 10GPa, Happroximately equals 0.5GPa for the 10nm thin platinum layer, Eapproximately equals 130GPa, Happroximately equals GPa for a 100nm thin gold layer, and Eapproximately equals 230GPa, Happroximately equals 13GPa for the LiNbO3 substrate. Moreover, platinum delaminates from titanium at critical normal load Lc1approximately equals 15$mnN, and its presence decreases the critical load Lc2, required to detach titanium from LiNbO3 substrate from Lc2approximately equals 50(mu) N to Lc2approximately equals 45(mu) N. The practical adhesion in the interface at the substrate and Pt-Ti layers has been also studied by scratching technique, using cube corner diamond tip. The scratch test was combined wiht examination of the scratch track morphology and the interface between Ti/Pt thin fils and substrate by scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), and the correlation of the films failure with the adhesion strength was investigated. Scratch tests reveal also, a decrease of the value of adhesion strength at titanium and substrate interface from Lc2approximately equals 4mN to L2approximately equals 3.5mN when Pt is evaporated on the Ti layer.
